The present invention relates to microwave waveguide coupling devices, and more particularly to TE.sub.21 circular waveguide couplers.
Prior art TE.sub.21 coupler designs employ four auxiliary rectangular waveguide lines symmetrically oriented around the main line circular waveguide to excite or receive a TE.sub.21 mode. These lines are subsequently connected to a 1:4 power distribution network. To convert this coupler to a circularly polarized TE.sub.21 mode, two sets of four auxiliary lines and two sets of 1:4 power distribution networks are required.
In other words, current TE.sub.21 circular waveguide couplers employ eight auxiliary rectangular waveguides to receive a circularly polarized TE.sub.21 circular waveguide mode, and two sets of 1:4 power combining circuitries and a quadrature hybrid are required to combine the outputs from the eight auxiliary coupler lines.
The disclosed invention, on the other hand, employs only one or two auxiliary lines for each TE.sub.21 mode excitation in the circular waveguide. With a single auxiliary line, no distribution network is required. For a two line coupler, a 1:2 power distribution network is required. The choice of a single or dual auxiliary line coupler depends on the length of the coupler and the coupling factor of the auxiliary coupling lines. If length is not a consideration, then a single line coupler is employed. A dual line coupler is used where it is required to constrain the coupler length. The main advantage gained is the significant reduction in the complexity and construction and hence, the cost of the power divider and feed circuitry.
The modified coupler design uses only two, or at the most, four auxiliary lines to achieve the same capabilities and performance of the TE.sub.21 circular waveguide coupler. This reduces the complexity of the combining circuitry. For a two auxiliary line coupler, only a quadrature hybrid is required. For a four auxiliary line coupler, two sets of 1:2 combiners and a quadrature hybrid are required.